The present invention relates to a mixer assembly of the cavity-transfer type for use in extrusion of a mix of polymers in conjunction with the extruder screw of a polymer extruder. More specifically, the subject invention is directed to a mixer component provided adjacent the downstream end of an extruder screw and including a motor driven rotor coaxially positioned downstream relative to the extruder screw within the heated barrel of an extruder assembly. A floating sleeve is positioned over the rotor and facing the inner surface of the barrel and includes transfer openings in its outer surface for receiving heated mix from the rotor which is directed into contact with the inner surface of the barrel and then returned through apertures in the floating sleeve to cavities provided in the outer surface of the rotor.
Cavity transfer type extruder devices have been employed in the past as exemplified by British Patent Specification No. 930,339 which discloses a hollow cylindrical stator member and a cylindrical rotor member which is mounted for rotation within the stator. The facing cylindrical surfaces on the rotor and the stator carrier respective pluralities of rows of elongated longitudinally extending grooves or apertures arranged peripherally around each member and are spaced axially along each member in parallel relationship. The annularly extending rows of grooves on the outer surface of the rotor are offset relative to the annular rows of grooves on the cylindrical stator member.
The foregoing arrangement is such that the overlapping closed cavities on the rotor and the stator cause the molten material to progressively move annually along the length of the mixer to effect a thorough mixing of the components thereof Additionally, a similarly known machine of the foregoing type is described in British Patent Specification No. 1,475,216.
Applicant's earlier U.S. Pat. No. 4,779,989 discloses a stator bore provided with a plurality of curved inwardly facing grooves surrounding an inner driven rotor member also provided with a plurality of curved grooves on its outer surface. The stator elements of Applicant's aforementioned patent are fixedly positioned relative to the barrel housing in which they are mounted.
A different approach is revealed in U.S. Pat. No. 5,013,233 of Semmekrot which discloses a driven rotor provided with a plurality of dimple type cavities 22 and 23 arranged in annular rows and axial rows which sequentially move into alignment with openings 27 in a floating ring 9.
Other prior art approaches to the mixing of molten polymer components are disclosed in British Patent No. 1,475,216, European Patent Application No. 81304235.5 and U.S. Pat. No. 4,746,478.
While the aforementioned and other prior art devices have provided varying degrees of performance, they have uniformly been expensive and costly to manufacture. Additionally, they have not been easily adaptable to conventional extruder screw means without special and expensive machining and design considerations. Moreover, the industry has continuously demanded ever increasing production capability and mixing thoroughness beyond that of the prior known devices.
Therefore, it is a primary object of the present invention to provide a new and approved polymer mixing apparatus and method that is economical to fabricate while providing large flow capacities and optimum mixing results.
Additional objects, advantages and capabilities of the present invention will become apparent from the following detailed description which should be considered in conjunction with the accompanying drawings illustrating the preferred embodiment of the invention, as well as certain variations therefrom.